Joining Naoki Sakurada's Gutsman team, Sakurai made his professional debut in Shooto on October 4, 1996 by submitting Caol Uno. Over the next five years he would go undefeated in eighteen bouts, representing the promotion in three consecutive victories at the renowned Vale Tudo Japan event, as well as French MMA promotion Golden Trophy 1999. Hayato would also win that organization's Shooto Middleweight Champion from Jutaro Nakao, which he defended before Tetsuji Kato.

In a less official light, he contended with Rumina Sato for the fastest victory at the time, knocking out Ademir Oliveira with a spectacular flying knee in 0:34 seconds moments before Sato beat him with a flying armbar in 0:08 against Charles Diaz.[4]

During his final times on the company, Sakurai also faced future UFC challenger Frank Trigg in an exciting battle. The two brawled in the clinch, with Trigg landing knees while Hayato threw punches and kicks to the body and leg; at one instance, Trigg almost knocked out Sakurai, stunning him and landing multiple undefended punches both standing and on the ground which drew blood. Trigg continued dominating through the second round, until Sakurai finally came back knocking him down with a left hook, and he managed to finish the fight with multiple knee strikes to the face, winning by KO.[5]

In August 2001, Sakurai was finally defeated by future longtime UFC Middleweight ChampionAnderson Silva, losing his championship title. After the loss, and subsequent to a severe car accident, Sakurai stopped fighting for Shooto full-time.

On March 22, 2002, Sakurai stepped into Ultimate Fighting Championship to fight the UFC Welterweight ChampionMatt Hughes at UFC 36. Hughes started the match taking down Sakurai repeatedly, but the Japanese worked submission attempts from the bottom and managed to capture Hughes's back. The second round saw Hayato landing a solid left hand and a knee to the head, which Hughes got back on the third by slamming the Japanese hard on the mat with a takedown and landing several strikes on the ground. The fourth would see the final action, with Hughes managing to knock down Sakurai and perform ground and pound until the referee stopped the fight.

After losing to Hughes, Sakurai fought periodically in Shooto and DEEP before joining PRIDE Fighting Championships, Japan's largest MMA organization. During this time he was inconsistent in his performances, often losing to much lower-ranked opponents. He also attempted to fight at 183 lb (83 kg)., but it was clear that his frame was far too small for that weight, and his performances suffered. Some speculated Sakurai's seeming loss of spirit and mental focus came from his infamous car accident he suffered after fighting Silva.[6]

Sakurai made an underwhelming debut before Daiju Takase in PRIDE Shockwave 2003. Takase controlled a part of the first round, taking down Sakurai and bloodying his nose with punches. At this point, however, Mach started coming back, hijacking the standing segments with superior striking and negating Takase's submission attempts in order to do damage through his guard. The Shooto fighter ended the fight taking down Takase several times and controlling the action, which gained him a unanimous decision.

In his next apparitions for PRIDE Bushido, Sakurai would face two members of the Gracie family, Rodrigo and Crosley, but he was unsuccessful in both ventures. He fought an uneventful match against the former, stopping him from passing guard for the first round and being stopped himself from passing guard in the second, before receiving some knees to the head which gained Gracie the decision; and he then lost by submission to the latter, despite him showing a better performance until the last minutes.

The match with Pulver was specially acclaimed, as it featured high speed and an exciting give and take. Sakurai peppered his opponent with strikes and kicks before receiving a left hand which seemed to put him down. He recovered and injured Pulver's eye with a combo, only to immediately land a front kick directly to the same eye, but then Hayato received another sudden left hook, which anticipated a possible finish. However, for a second time, Sakurai came back and pressed action, finally bringing him down with a body shot and a knee strike for the TKO. The bout was called "awesome" and "Fight of the Year Contender-level" by analyst Scott Newman.[7] Similarly back and forth would be the fight against Hansen: the two fighters exchanged strikes, hip throws and leglocks through the entire bout, while Sakurai landed spinning back kicks and a close armbar attempt. Sakurai got the decision win, and it set off a match in the finals against Takanori Gomi, Sakurai's former colleague and training partner.

On December 31, 2005 Sakurai fought Gomi for the first ever PRIDE Fighting Championships 160 lb (73 kg) championship of the world. Although fighting with a torn ACL he suffered in training just three weeks prior to the fight, though this was not known outside of his coaching circle at the time, Sakurai initially had the upper-hand, pounding Gomi with brutal inside-leg kicks. A few minutes into the round Sakurai attempted a judo throw, but the ring ropes got in the way and caused him to crash head first on the mat with Gomi taking his back. Takanori capitalized and rained down punches on him, and although Sakurai was able to return to his feet, he was overwhelmed and knocked out with a punching combo.

Despite the loss to Gomi, Sakurai would continue to impress with his performances. At Bushido 11 he scored a brutal knockout over WEC veteran Olaf Alfonso.[8] On August 26, 2006, Mach fought Brazilian Luciano Azevedo at Bushido 12. After several minutes of attempted ground and pound by Azevedo, the fighters were stood back up. Mach then consistently stuffed Azevedo's takedowns, and landed a fight-ending knee on Azevedo over his left eye. The fight was stopped, TKO by cut.

After PRIDE's folding, Sakurai joined its offshoot promotion DREAM, in whose Welterweight Grand Prix he took part. He faced top-ranked lightweight Shinya Aoki at DREAM 8 in a match with revenge overtones, as Sakurai had defeated Aoki back in Shooto in what was called a controversial decision. This time, Sakurai won in impressive fashion, sweeping over a charging Aoki and delivering knees to the head and punches for a KO at 0:27. He then lost at DREAM 10 in the semi-final of the tournament to eventual winner Marius Zaromskis in a huge upset, conceding the loss via knockout from a head kick and punches.

Almost a year later, Sakurai returned to face Jae Suk Lim at Mach Dojo / Gladiator: Mach Festival. Sakurai lost by TKO in the first round.

He competed in the Tokyo International Jiu-Jitsu Open Championship 2009, ranking himself as a Brazilian jiu-jitsublack belt for his grappling expertise. He opened the first round against Akira Uemura, but was eliminated.

Sakurai was renowned for his well rounded set of skills, excelling on every field of the MMA game. On the stand-up, he favoured grinding low kicks and an advanced boxing, along with a wide usage of knee strikes, including flying knees.[6] A prolific clinch user, although he was not a high level judoka, Sakurai excelled in performing hip throws during his matches, favouring o goshi, uki goshi and ippon seoi nage.[6] Finally, his grappling technique was one of his biggest strengths, using his shoot wrestling expertise to great effect. He was the only user of this discipline in reaching the ADCC finals both in his weight and absolute division,[6] submitting heavier and more decorated grapplers like Ricco Rodriguez and Vinny Magalhães.